Although ES is needed by humans and originated because of social concerns, ES itself seeks to improve human
welfare by protecting NC. As contrasted with economic capital, NC consists of water, land, air, minerals and
ecosystem services, hence much is converted to manufactured or economic capital. Environment includes the
sources of raw materials used for human needs, and ensuring that sink capacities recycling human wastes are not
exceeded, in order to prevent harm to humans
ž Humanity must learn to live within the limitations of the biophysical environment. ES means NC must be
maintained, both as a provider of inputs (sources), and as a sink for wastes. This means holding the scale of the
human economic subsystem (D population ð consumption, at any given level of technology) to within the
biophysical limits of the overall ecosystem on which it depends. ES needs sustainable consumption by a stable
population
ž On the sink side, this translates into holding waste emissions within the assimilative capacity of the environment
without impairing it
ž On the source side, harvest rates of renewables must be kept within regeneration rates
ž Technology can promote or demote ES. Non-renewables cannot be made sustainable, but quasi-ES can be
approached for non-renewables by holding their depletion rates equal to the rate at which renewable substitutes
are created. There are no substitutes for most environmental services, and there is much irreversibility if they are
damaged